Self-planarized deep trench process for self-aligned nitride bipolar device isolation

The self-planarization of deep trench with 2 micron thick field oxidation has been developed for self-aligned nitride bipolar integrated circuit fabrication. Trenches with geometry of 2 μm wide by 8 μm deep were achieved by anisotropic etching for isolating global buried collectors. They were then filled and planarized simply by a local oxidation of silicon (LOCOS) without polysilicon re-filling or etching back, while maintained a collector-to-collector leakage of 5 μa at 15 V. As proof-of-technology, arrays of trench-isolated bipolar transistors with cut-off frequency of 14 GHz were gold-metallized without extra planarization of the trench.